The overall goal of this project is to discover the mechanism and control of the secretion and resorption of moutling fluid in insects. The study will be conducted during the larval-pupal transformation in Saturniid and Sphyngid insects, where it can be studied by rigorous biophysical and biochemical techniques, such as short-circuiting, unidirectional flux determinations and flux ratio analysis, and by competition with other mono-valent and di-valent cations and anions. Properties of potassium transport during secretion and bicarbonate transport during secretion and resorption of moulting fluid across the pharate pupal integument (PPI) will be studied, as will the effects of divalent metal cations on this transport. The nature of insect potassium and bicarbonate specific ATPases, and potassium specific ionophoroproteins will be investigated and their patterns of change correlated with the capacity of the PPI to actively transport potassium and bicarbonate. The contribution of gamma-aminobutyric acid to the expression of morphogenetic hormones such as ecdysone and/or juvenile hormone on the epidermis will also be studied in the context of moulting. This system will be used as a model for moulting events in vector insects and pests, where it has medical and environmental value.